In a wireless communication system, some standards for a physical (PHY) layer define a structured data sequence having a fixed duration called a frame or radio frame, for communication between a user equipment (UE) and an evolved node B (eNB). One frame may include a predetermined number of time resource units. A time resource unit is referred to as a subframe or slot. One subframe/slot may be configured to include a plurality of orthogonal frequency division multiplexing (OFDM) symbols in the time domain. For example, one subframe may be configured by one or more slots each including a plurality of OFDM symbols. The number of subframes per frame, the number of slots per subframe, and the number of OFDM symbols per slot are determined according to physical standards of the system.
FIG. 1 schematically illustrates three duplex schemes used in bidirectional radio communication.
Uplink (UL)/downlink (DL) configuration in a frame varies with a duplexing scheme. Duplex refers to bidirectional communication between two devices, distinguished from simplex indicating unidirectional communication. In bidirectional communication, transmission on bidirectional links may occur at the same time (full-duplex) or at separate times (half-duplex).
Referring to FIG. 1, a full-duplex transceiver is used to separate two communication links of opposite directions in the frequency domain. That is, different carrier frequencies are adopted in respective link directions. Duplex using different carrier frequencies in respective link directions is referred to as frequency division duplex (FDD). Conversely, a half-duplex transceiver is used to separate two communication links of opposite directions in the time domain. Referring to FIG. 1, duplex using the same carrier frequency in respective link directions is referred to as time division duplex (TDD). Referring to FIG. 1, the half-duplex transceiver may use different carrier frequencies in respective link directions and this is referred to as half duplex FDD (HD-FDD). In HD-FDD, communication of opposite directions for a specific device occurs not only on different carrier frequencies but also at different timings. Therefore, HD-FDD is regarded as a hybrid of FDD and TDD.
Since transmission and reception cannot be simultaneously performed in HD-FDD and TDD, a time resource for transmission and a time resource for reception need to be properly distributed.